Assessment of Sea Otter (Enhydra lutris kenyoni) Diet in Kachemak Bay, Alaska (2008-2010)

Long-term monitoring of a keystone species’ diet contributes to our understanding of shifts in the structure of an ecosystem. Sea otters were extirpated from Kachemak Bay, Alaska by 1911 and returned to the region through natural recolonization beginning in the 1970s. The sea otter population increased from <1,000 in the 1990s to 3,600 in 2008. In Kachemak Bay we describe the diet based on results from scat analyses and visual observation. Scat collection is only feasible in winter months and analysis is biased toward species where hard parts of prey are ingested. Scats were collected over a one-week period October - May during 2008-10. Dominant prey types for all samples combined were mussel (41%), crab (32%), and clam (12%). The combined proportion of these prey observed visually were clam (38%), mussel (14%) and crab (2%). Scat analysis will be a useful tool in identifying trends in winter consumption of crab and mussel, but will exclude identification of larger bivalve and soft-bodied prey. Kachemak Bay is primarily a soft-sediment benthic habitat, which is suitable habitat for clams and crabs. In the 1970s, commercially valuable crab and clam species were abundant in this area. We evaluate scat analysis as a low-cost tool to monitor long-term trends in the winter diet for sea otters in Kachemak Bay.